JP7532969B2 - Laminated film and conductive substrate - Google Patents

Description

The present invention relates to a laminated film and a conductive substrate.

The speed and capacity of signals used in electronic devices such as mobile phones, their base station equipment, network infrastructure equipment such as servers and routers, and large computers are increasing year by year. As a result, the printed wiring boards installed in these electronic devices must be able to handle higher frequencies, and there is a demand for board materials with low dielectric constants and low dielectric tangents that enable reduced transmission loss. In recent years, in addition to the electronic devices mentioned above, new systems that handle high-frequency wireless signals in the ITS field (related to automobiles and transportation systems) and in the indoor short-range communication field have been put into practical use and are planned to be put into practical use as applications that handle such high-frequency signals. It is expected that in the future, there will be an even greater demand for low-transmission-loss board materials for the printed wiring boards installed in these devices.

Conventionally, resins such as polyphenylene ether (PPE), polyimide (PI), liquid crystal polymer (LCP), and fluororesin have been used for printed wiring boards that require low transmission loss (see, for example, Patent Documents 1 to 4).

Japanese Unexamined Patent Publication No. 58-69046 JP 2012-255059 A JP 2014-60449 A JP 2003-171480 A

Fluorine resin is known to be a material with low dielectric properties, but has low adhesion to conductor foil. Liquid crystal polymers have a high melting point, so hot pressing at a high temperature of 300°C or higher is required to manufacture wiring boards containing liquid crystal polymers. It is possible to use a flexible resin material with excellent adhesion to adhere to the conductor foil, but flexible resin materials with excellent adhesion tend to have poor flame retardancy, which is required for printed wiring boards. Therefore, there is a demand for a resin film that combines low dielectric properties, adhesion, and flame retardancy.

The present invention aims to provide a laminated film having adhesive properties, low dielectric properties, and flame retardancy, and a conductive substrate using the laminated film.

One aspect of the present disclosure relates to a laminated film comprising a base film and resin layers provided on both sides of the base film, the base film being a liquid crystal polymer film or a fluororesin film, and the resin layer including a resin composition containing a rubber component, a crosslinking component having an epoxy group, a curing agent, a bromine-based flame retardant, and a flame retardant assistant.

Another aspect of the present disclosure relates to a conductive substrate having a base film, a cured resin layer provided on both sides of the base film, and a conductive foil provided on at least one side of the cured resin layer opposite the base film, in which the base film is a liquid crystal polymer film or a fluororesin film, and the cured resin layer includes a cured product of a resin composition containing a rubber component, a crosslinking component having an epoxy group, a curing agent, a bromine-based flame retardant, and a flame retardant auxiliary.

The present invention provides a laminated film having adhesive properties, low dielectric properties, and flame retardancy, and a conductive substrate using the laminated film.

FIG. 1 is a schematic cross-sectional view showing one embodiment of a laminated film.

Several embodiments of the present invention are described in detail below. However, the present invention is not limited to the following embodiments.

[Laminated film]
A laminate film according to an embodiment of the present invention includes a base film and a resin layer provided on both sides of the base film. Fig. 1 is a schematic cross-sectional view showing an embodiment of the laminate film. The laminate film 10 includes a base film 1 and a resin layer 3 provided on both sides of the base film 1.

(Base film)
The dielectric properties can be improved by using a liquid crystal polymer film or a fluororesin film as the base film according to this embodiment. The thickness of the base film 1 may be 30 μm or more, 50 μm or more, or 80 μm or more, and may be 250 μm or less, 200 μm or less, or 150 μm or less.

A liquid crystal polymer film (hereinafter sometimes simply referred to as "LCP film") is a molded product of a liquid crystal polymer. The liquid crystal polymer constituting the liquid crystal polymer film may be a thermotropic liquid crystal polymer that exhibits liquid crystallinity in a molten state. Examples of thermotropic liquid crystal polymers include thermotropic liquid crystal polyesters and thermotropic liquid crystal polyester amides. A structure selected from an imide bond, a urethane bond, a carbodiimide bond, a carbonate bond, and an isocyanurate bond may be introduced into the thermotropic liquid crystal polyesters and thermotropic liquid crystal polyester amides. The liquid crystal polymer may be a polymer containing a constituent unit derived from p-hydroxybenzoic acid and/or a constituent unit derived from 6-hydroxy-2-naphthoic acid.

The liquid crystal polymer film may further contain a polymer other than the liquid crystal polymer, provided that the dielectric properties are not excessively impaired. The polymer other than the liquid crystal polymer may be a polymer having a melting point of 220°C or higher, or 280 to 360°C, and examples thereof include polyetheretherketone, polyethersulfone, polyimide, polyetherimide, polyamide, polyamideimide, and polyarylate.

Examples of fluororesins that make up the fluororesin film include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-perfluoroalkoxyethylene polymer (PFE), tetrafluoroethylene-hexafluoropropylene polymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). The fluororesin film is preferably a film containing polytetrafluoroethylene, as this has superior high-frequency characteristics.

(Resin Layer)
The resin layer includes a resin composition that contains a rubber component, a cross-linking component having an epoxy group, a curing agent, a bromine-based flame retardant, and a flame retardant auxiliary.

The resin layer is easily given flexibility mainly by the rubber component. The rubber component may contain at least one rubber selected from the group consisting of, for example, acrylic rubber, isoprene rubber, butyl rubber, styrene butadiene rubber, butadiene rubber, acrylonitrile butadiene rubber, silicone rubber, urethane rubber, chloroprene rubber, ethylene propylene rubber, fluororubber, vulcanized rubber, epichlorohydrin rubber, and chlorinated butyl rubber. From the viewpoint of protecting the wiring from damage caused by moisture absorption, etc., a rubber component with low gas permeability may be used. From this viewpoint, the rubber component may contain at least one rubber selected from styrene butadiene rubber, butadiene rubber, and butyl rubber. By using styrene butadiene rubber, the resistance of the resin layer to various chemicals used in the plating process is improved, and wiring boards can be manufactured with a good yield.

Examples of commercially available acrylic rubbers include the "Nipol AR Series" from Nippon Zeon Co., Ltd. and the "Clarity Series" from Kuraray Co., Ltd. Examples of commercially available isoprene rubbers include the "Nipol IR Series" from Nippon Zeon Co., Ltd. Examples of commercially available butyl rubbers include the "BUTYL Series" from JSR Corporation Examples of commercially available styrene butadiene rubbers include the "Dynaron SEBS Series" and "Dynaron HSBR Series" from JSR Corporation, the "Craton D Polymer Series" from Clayton Polymer Japan Co., Ltd., and the "AR Series" from Aronkasei Co., Ltd. Examples of commercially available butadiene rubbers include the "Nipol BR Series" from Nippon Zeon Co., Ltd. Examples of commercially available acrylonitrile butadiene rubbers include the "JSR NBR Series" from JSR Corporation. Examples of commercially available silicone rubbers include the "KMP Series" from Shin-Etsu Silicone Co., Ltd. Commercially available ethylene propylene rubber products include, for example, the "JSR EP Series" from JSR Corporation. Commercially available fluororubber products include, for example, the "Dai-El Series" from Daikin Corporation. Commercially available epichlorohydrin rubber products include, for example, the "Hydrin Series" from Zeon Corporation.

Rubber components can also be produced synthetically. For example, acrylic rubber is obtained by reacting (meth)acrylic acid, (meth)acrylic acid esters, aromatic vinyl compounds, vinyl cyanide compounds, etc.

The rubber component may contain a rubber having a crosslinking group. The use of a rubber having a crosslinking group tends to improve the heat resistance of the elastic resin layer. The crosslinking group may be a reactive group that can proceed with a reaction that crosslinks the molecular chains of the rubber component. Examples of such a group include the reactive groups of a crosslinking component having an epoxy group, which will be described later, an acid anhydride group, an amino group, a hydroxyl group, an epoxy group, and a carboxyl group.

The rubber component may contain a rubber having at least one of the crosslinking groups of an acid anhydride group or a carboxyl group. An example of a rubber having an acid anhydride group is a rubber partially modified with maleic anhydride. The rubber partially modified with maleic anhydride is a polymer containing structural units derived from maleic anhydride. An example of a commercially available product of rubber partially modified with maleic anhydride is the styrene-based elastomer "Tufprene 912" manufactured by Asahi Kasei Corporation.

The rubber partially modified with maleic anhydride may be a hydrogenated styrene-based elastomer partially modified with maleic anhydride. Hydrogenated styrene-based elastomers are also expected to have effects such as improved weather resistance. Hydrogenated styrene-based elastomers are elastomers obtained by adding hydrogen to the unsaturated double bonds of a styrene-based elastomer having a soft segment containing an unsaturated double bond. Commercially available hydrogenated styrene-based elastomers partially modified with maleic anhydride include "FG1901" and "FG1924" from Kraton Polymer Japan Co., Ltd., and "Tuftec M1911", "Tuftec M1913", and "Tuftec M1943" from Asahi Kasei Corporation.

The weight average molecular weight (Mw) of the rubber component may be 20,000 to 200,000, 30,000 to 150,000, or 50,000 to 125,000 from the viewpoint of coating properties. Mw here refers to the standard polystyrene equivalent value determined by gel permeation chromatography (GPC).

In the resin composition, the content of the rubber component is preferably 60 to 95% by mass, more preferably 65 to 90% by mass, and even more preferably 70 to 85% by mass, based on the total amount of the rubber component, the cross-linking component having an epoxy group, and the curing agent. When the content of the rubber component is 60% by mass or more, more sufficient elasticity is easily obtained, and the rubber component and the cross-linking component tend to mix well. When the content of the rubber component is 95% by mass or less, the resin layer tends to have particularly excellent properties in terms of adhesion, insulation reliability, and heat resistance. The content of the rubber component in the resin layer may be within the above range based on the mass of the resin layer.

The cross-linking component having an epoxy group (hereinafter, sometimes simply referred to as "cross-linking component") is a component that cross-links during a curing reaction to form a cross-linked polymer. The cross-linking component is not particularly limited as long as it has an epoxy group in the molecule, and can be, for example, a general epoxy resin. The epoxy resin may be monofunctional, bifunctional, or polyfunctional, and is not particularly limited, but a bifunctional or polyfunctional epoxy resin may be used to obtain sufficient curability.

Epoxy resins include bisphenol A type, bisphenol F type, phenol novolac type, naphthalene type, dicyclopentadiene type, cresol novolac type, and other epoxy resins. Epoxy resins modified with an aliphatic chain can impart flexibility. An example of a commercially available aliphatic chain modified epoxy resin is EXA-4816 manufactured by DIC Corporation. From the viewpoints of curability, low tackiness, and heat resistance, phenol novolac type, cresol novolac type, naphthalene type, or dicyclopentadiene type epoxy resins may be selected. These epoxy resins may be used alone or in combination of two or more types.

The combination of a rubber having a maleic anhydride group or a carboxyl group with a compound having an epoxy group (epoxy resin) provides particularly excellent effects in terms of the heat resistance and low moisture permeability of the elastic resin layer, adhesion between the elastic resin layer and the conductive layer, and low tack of the elastic resin layer. Improved heat resistance of the elastic resin layer can suppress deterioration of the elastic resin layer during a heating process such as nitrogen reflow. Low tack of the elastic resin layer allows for easy handling of the conductor board or wiring board.

The resin composition may contain other crosslinking components other than the crosslinking component having an epoxy group, as long as the effect of the present invention is not significantly impaired. From the viewpoint of more sufficiently reducing the dielectric tangent of the elastic resin layer, the content of the other crosslinking components is preferably less than 10 parts by mass per 100 parts by mass of the crosslinking component having an epoxy group.

The curing agent is a compound that is itself involved in the curing reaction, and can reduce the dielectric tangent while improving the heat resistance of the resin layer.

The curing agent is not particularly limited, but from the viewpoint of more fully obtaining the effect of improving heat resistance and the effect of reducing the dielectric tangent, an ester-based curing agent can be used. Examples of ester-based curing agents include compounds having one or more highly reactive ester groups in one molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds. Examples of commercially available ester-based curing agents include "EPICLON HPC8000-65T", "EPICLON HPC8000-L-65MT", and "EPICLON HPC8150-60T" (all trade names manufactured by DIC Corporation). These can be used alone or in combination of two or more.

During the curing reaction, the ester-based curing agent is thought to react with the crosslinking component as shown in the following formula (I). In the reaction between such an ester-based curing agent and the crosslinking component, no hydroxyl groups are produced, and even if a side reaction occurs, hydroxyl groups are unlikely to be produced. As a result, it is thought that a low dielectric tangent can be achieved.

式中、Ｒ^１、Ｒ^２及びＲ^３はそれぞれ独立に、１価の有機基を示すが、本発明の効果がより十分に得られることから、芳香環を有する１価の有機基であってもよい。

In the formula, R ¹ , R ² and R ³ each independently represent a monovalent organic group, but may be a monovalent organic group having an aromatic ring, since this allows the effects of the present invention to be more fully obtained.

In the resin composition, the total content of the crosslinking component and the curing agent is preferably 5 to 40 mass %, more preferably 10 to 35 mass %, and even more preferably 15 to 30 mass %, based on the total amount of the rubber component, the crosslinking component, and the curing agent. When the total content of the crosslinking component and the curing agent is 5 mass % or more, more sufficient curing is easily obtained, and the resin layer tends to have particularly excellent properties in terms of adhesion, insulation reliability, and heat resistance. When the total content of the crosslinking component and the curing agent is 40 mass % or less, more sufficient elasticity is easily obtained, and the rubber component and the crosslinking component tend to mix well.

In the resin composition, the content ratio of the crosslinking component to the curing agent is preferably in the range of 4:5 to 5:4, in terms of the equivalent ratio of the epoxy groups in the epoxy resin to the ester bonds in the ester-based curing agent. By having the content ratio within the above range, more sufficient curing is easily achieved, and the elastic resin layer tends to have particularly excellent properties in terms of adhesion, insulation reliability, and heat resistance.

The resin layer contains both a brominated flame retardant and a flame retardant assistant, making it possible to produce a laminated film that is self-extinguishing and has excellent flame retardancy.

The bromine-based flame retardant may include a compound having an aromatic ring to which a bromine atom is bonded, or may include a compound having a triazine skeleton. From the viewpoint of improving dielectric properties, the bromine-based flame retardant preferably includes a compound having an aromatic ring to which a bromine atom is bonded and a triazine skeleton. One type of bromine-based flame retardant may be used alone, or two or more types may be used in combination.

Examples of brominated flame retardants include brominated additive flame retardants such as hexabromobenzene, pentabromotoluene, ethylene bis(pentabromophenyl), ethylene bistetrabromophthalimide, 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane, tetrabromocyclooctane, hexabromocyclododecane, bis(tribromophenoxy)ethane, brominated polyphenylene ether, brominated polystyrene, and 2,4,6-tris(tribromophenoxy)-1,3,5-triazine; and brominated reaction flame retardants containing unsaturated double bond groups, such as tribromophenylmaleimide, tribromophenylacrylate, tribromophenylmethacrylate, tetrabromobisphenol A dimethacrylate, pentabromobenzylacrylate, and brominated styrene.

From the viewpoint of the balance between flame retardancy and flexibility, the content of the bromine-based flame retardant may be 1 to 30 parts by mass, 2 to 25 parts by mass, or 4 to 20 parts by mass per 100 parts by mass of the total amount of the rubber component, the cross-linking component, and the curing agent.

As a flame retardant auxiliary, for example, an antimony compound can be used. Examples of antimony compounds include antimony trioxide, antimony pentoxide, and sodium antimonate.

From the viewpoint of the balance between flame retardancy and flexibility, the content of the flame retardant auxiliary may be 1 to 20 parts by mass, 2 to 18 parts by mass, or 4 to 16 parts by mass per 100 parts by mass of the total amount of the rubber component, the cross-linking component, and the curing agent.

The resin composition may further contain a curing accelerator. The curing accelerator is a compound that functions as a catalyst for the curing reaction. The curing accelerator may be selected from tertiary amines, imidazoles, organic acid metal salts, phosphorus compounds, Lewis acids, amine complex salts, and phosphines. Among these, imidazole may be used from the viewpoint of storage stability and curing properties of the varnish of the resin composition. When the rubber component contains rubber partially modified with maleic anhydride, an imidazole compatible with this may be selected.

In the resin composition, the content of the curing accelerator may be 0.1 to 10 parts by mass relative to 100 parts by mass of the total amount of the rubber component, the cross-linking component, and the curing agent. If the content of the curing accelerator is 0.1 parts by mass or more, there is a tendency that more sufficient curing is easily obtained. If the content of the curing accelerator is 10 parts by mass or less, there is a tendency that more sufficient heat resistance is easily obtained. From the above viewpoints, the content of the curing accelerator may be 0.3 to 7 parts by mass, or 0.5 to 5 parts by mass.

In addition to the above components, the resin composition may further contain antioxidants, anti-yellowing agents, ultraviolet absorbers, visible light absorbers, colorants, plasticizers, stabilizers, fillers, leveling agents, etc., as necessary, to the extent that the effects of the present invention are not significantly impaired.

The thickness of the resin layer is not particularly limited, but may be 1 to 100 μm, 2 to 60 μm, 3 to 40 μm, or 4 to 20 μm from the viewpoint of the balance between the flame retardancy and flexibility of the laminated film.

The elastic modulus (tensile elastic modulus) of the resin layer after curing may be 0.1 MPa or more and 1000 MPa or less. If the elastic modulus is 0.1 MPa or more and 1000 MPa or less, the handleability and flexibility as a substrate tend to be particularly excellent. From this viewpoint, the elastic modulus may be 0.3 MPa or more and 100 MPa or less, or 0.5 MPa or more and 50 MPa or less.

The breaking elongation of the cured resin layer may be 100% or more. If the breaking elongation is 100% or more, sufficient elasticity tends to be obtained. From this viewpoint, the breaking elongation may be 150% or more, 200% or more, 300% or more, or 500% or more. The upper limit of the breaking elongation is not particularly limited, but is usually about 1000% or less.

The dielectric loss tangent (Df) of the cured resin layer may be 0.004 or less, 0.0035 or less, 0.003 or less, or 0.0025 or less, from the viewpoint of sufficiently reducing the transmission loss of the wiring pattern provided on the resin layer. The lower limit of the dielectric loss tangent is not particularly limited, but is usually about 0.0005 or more.

The dielectric constant (Dk) of the cured resin layer may be 3.0 or less, 2.8 or less, or 2.5 or less, from the viewpoint of sufficiently reducing the transmission loss of the wiring pattern provided on the resin layer.

The resin layer can be formed, for example, by dissolving or dispersing a rubber component, a crosslinking component, a curing agent, a bromine-based flame retardant, a flame retardant assistant, and other components as necessary in an organic solvent to prepare a resin varnish, and then forming the resin varnish onto a carrier film to produce a resin film.

The organic solvent is not particularly limited, but examples thereof include aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene, and p-cymene; cyclic ethers such as tetrahydrofuran and 1,4-dioxane; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and 4-hydroxy-4-methyl-2-pentanone; esters such as methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, and γ-butyrolactone; carbonates such as ethylene carbonate and propylene carbonate; and amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. From the viewpoint of solubility and boiling point, toluene or N,N-dimethylacetamide may be used. These organic solvents may be used alone or in combination of two or more kinds. The solid content (components other than the organic solvent) concentration in the resin varnish may be 20 to 80% by mass.

The carrier film is not particularly limited, but examples thereof include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; and films of polycarbonate, polyamide, polyimide, polyamideimide, polyetherimide, polyethersulfide, polyethersulfone, polyetherketone, polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, and liquid crystal polymers. Among these, from the viewpoint of flexibility and toughness, films of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polypropylene, polycarbonate, polyamide, polyimide, polyamideimide, polyphenylene ether, polyphenylene sulfide, polyarylate, or polysulfone may be used as the carrier film.

The thickness of the carrier film is not particularly limited, but may be 3 to 250 μm. If the thickness of the carrier film is 3 μm or more, the film strength is sufficient, and if the thickness of the carrier film is 250 μm or less, sufficient flexibility is obtained. From the above viewpoints, the thickness may be 5 to 200 μm, or 7 to 150 μm. From the viewpoint of improving the peelability from the resin layer, a film in which the carrier film has been subjected to a release treatment using a silicone-based compound, a fluorine-containing compound, etc. may be used as necessary.

If necessary, a protective film may be attached onto the resin layer to form a three-layer resin film consisting of a carrier film, a resin layer, and a protective film.

The protective film is not particularly limited, and examples thereof include films of polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; and polyolefins such as polyethylene and polypropylene. Among these, from the viewpoint of flexibility and toughness, films of polyesters such as polyethylene terephthalate, and polyolefins such as polyethylene and polypropylene may be used as the protective film. From the viewpoint of improving peelability from the elastic resin layer, the protective film may be subjected to a release treatment using a silicone-based compound, a fluorine-containing compound, or the like.

The thickness of the protective film may vary depending on the desired flexibility, but may be 10 to 250 μm. A thickness of 10 μm or more tends to provide sufficient film strength, while a thickness of 250 μm or less tends to provide sufficient flexibility. From the above perspective, the thickness may be 15 to 200 μm, or 20 to 150 μm.

A laminated film can be produced, for example, by preparing two resin films, peeling off the protective films, and bonding the exposed resin layers to both sides of a base film.

[Conductor substrate]
The conductive substrate according to one embodiment has a base film, a cured resin layer provided on both sides of the base film, and a conductive foil provided on at least one side of the cured resin layer opposite to the base film. The base film is the above-mentioned liquid crystal polymer film or fluororesin film. The cured resin layer includes a cured product of a resin composition containing a rubber component, a crosslinking component having an epoxy group, a curing agent, a bromine-based flame retardant, and a flame retardant auxiliary. That is, the cured resin layer is a cured resin layer constituting the laminate film according to this embodiment.

The elastic modulus of the conductor foil may be 40 to 300 GPa. When the elastic modulus of the conductor foil is 40 to 300 GPa, the conductor foil is less likely to break due to elongation of the wiring board. From a similar perspective, the elastic modulus of the conductor foil may be 50 GPa or more or 60 GPa or more, and may be 280 GPa or less or 250 GPa or less. The elastic modulus of the conductor foil here may be a value measured by a resonance method.

The conductor foil may be a metal foil. Examples of the metal foil include copper foil, titanium foil, stainless steel foil, nickel foil, permalloy foil, 42 alloy foil, kovar foil, nichrome foil, beryllium copper foil, phosphor bronze foil, brass foil, nickel silver foil, aluminum foil, tin foil, lead foil, zinc foil, solder foil, iron foil, tantalum foil, niobium foil, molybdenum foil, zirconium foil, gold foil, silver foil, palladium foil, Monel foil, Inconel foil, and Hastelloy foil. From the viewpoint of appropriate elastic modulus, the conductor foil may be selected from copper foil, gold foil, nickel foil, and iron foil. From the viewpoint of wiring formability, the conductor foil may be copper foil. Copper foil can be easily formed into a wiring pattern by photolithography without impairing the properties of the elastic resin layer.

The copper foil is not particularly limited, and for example, electrolytic copper foil and rolled copper foil used for copper-clad laminates and flexible wiring boards can be used. Commercially available electrolytic copper foils include, for example, F0-WS-18 (manufactured by Furukawa Electric Co., Ltd., product name), NC-WS-20 (manufactured by Furukawa Electric Co., Ltd., product name), YGP-12 (manufactured by Nippon Denkai Co., Ltd., product name), GTS-18 (manufactured by Furukawa Electric Co., Ltd., product name), and F2-WS-12 (manufactured by Furukawa Electric Co., Ltd., product name). Rolled copper foils include, for example, TPC foil (manufactured by JX Metals Corporation, product name), HA foil (manufactured by JX Metals Corporation, product name), HA-V2 foil (manufactured by JX Metals Corporation, product name), and C1100R (manufactured by Mitsui Sumitomo Metal Mining Co., Ltd., product name). Copper foil that has been subjected to a roughening treatment may be used from the viewpoint of adhesion with the elastic resin layer. Rolled copper foil may be used from the viewpoint of folding resistance.

The metal foil may have a roughened surface formed by a roughening treatment. In this case, the metal foil is usually provided on the stretchable resin layer with the roughened surface facing the stretchable resin layer. From the viewpoint of adhesion between the stretchable resin layer and the metal foil, the surface roughness Ra of the roughened surface may be 0.1 to 3 μm, or 0.2 to 2.0 μm. To easily form fine wiring, the surface roughness Ra of the roughened surface may be 0.3 to 1.5 μm.

The surface roughness Ra can be measured, for example, using a surface profiler Wyko NT9100 (manufactured by Veeco) under the following conditions.
Measurement conditions: Internal lens: 1x External lens: 50x Measurement range: 0.120 x 0.095 mm
Measurement depth: 10 μm
Measurement method: Vertical scanning interferometry (VSI)

The thickness of the conductor foil is not particularly limited, but may be 1 to 50 μm. When the thickness of the conductor foil is 1 μm or more, the wiring pattern can be formed more easily. When the thickness of the conductor foil is 50 μm or less, etching and handling are particularly easy.

The conductor foil is provided on one or both sides of the resin layer. By providing the conductor foil on both sides of the resin layer, warping due to heating for curing, etc. can be suppressed.

There are no particular limitations on the method for providing the conductor foil, but examples include a method in which the resin composition for forming the cured resin layer is directly applied to the metal foil, and a method in which the resin layer and the conductor foil in a laminate film are laminated.

The above describes preferred embodiments of the present disclosure, but these are merely examples for the purpose of explaining the present invention, and are not intended to limit the scope of the present invention to these embodiments alone. The present invention can be implemented in various forms different from the above embodiments without departing from the spirit of the present invention.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

[Example 1]
(Preparation of resin varnish)
To a polyvinyl chloride bottle, 80 parts by mass (non-volatile content) of maleic anhydride modified hydrogenated styrene ethylene butadiene rubber (KRATON Corporation, product name "FG1924", styrene ratio: 1.3%), 10.9 parts by mass (non-volatile content) of dicyclopentadiene type epoxy resin (DIC Corporation, product name "EPICLON HP7200H"), 9.1 parts by mass (non-volatile content) of an ester-based curing agent (DIC Corporation, product name "HPC-8150"), and 400 parts by mass of toluene were added and mixed to obtain a base resin with a non-volatile content of 25% by mass. Next, 5 parts by mass of brominated aromatic triazine (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "SR-245"), 5 parts by mass of antimony trioxide (manufactured by Suzuhiro Chemical Co., Ltd., product name "Finecut WP-2"), and 3 parts by mass of 1-benzyl-2-methylimidazole (manufactured by Shikoku Kasei Kogyo Co., Ltd., product name "1B2MZ") were added to the base resin, and mixed using a planetary centrifugal mixer (manufactured by Thinky Corporation, product name "AR-100") to prepare a resin varnish.

(Preparation of resin film)
A release-treated polyethylene terephthalate (PET) film (manufactured by Teijin Film Solutions Co., Ltd., product name "Purex A31", thickness 25 μm) was prepared as a carrier film. The above-mentioned resin varnish was applied to the release-treated surface of this PET film using a knife coater (manufactured by Yasui Seiki Co., Ltd., product name "SNC-350"). The coating film was dried by heating at 80°C for 20 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., product name "MSO-80TPS") to form a resin layer having a predetermined thickness. A release-treated PET film identical to the carrier film was attached as a protective film to the formed resin layer with the release-treated surface facing the resin layer, to obtain a resin film.

(Preparation of Laminated Film)
A resin layer (thickness: 5 μm) obtained by peeling off the carrier film and protective film from the resin film was laminated on both sides of an LCP film (manufactured by Kuraray Co., Ltd., product name "CTQ", thickness: 100 μm), and laminated using a vacuum pressure laminator (manufactured by Nikko Materials Co., Ltd., product name "V130") under conditions of a pressure of 0.9 MPa, a temperature of 100° C., and a pressure time of 1 minute, to obtain a laminated film consisting of three layers: resin layer/LCP/resin layer.

[Examples 2 to 3 and Comparative Example 1]
Resin films and laminate films were prepared in the same manner as in Example 1, except that the amounts of brominated aromatic triazine, which is a brominated flame retardant, and antimony trioxide, which is a flame retardant assistant, were changed to the amounts (parts by mass) shown in Table 1 to prepare resin varnishes.

[evaluation]
The resin film and the laminated film were evaluated as follows. The results are shown in Table 1.

(Dielectric Properties)
The dielectric properties were evaluated by the Split Post Dielectric Reconator (SPDR) method. The resin film was heat-treated at 180°C for 60 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., product name "MSO-80TPS") to harden the resin layer and prepare a sample for measuring dielectric properties. The sample was placed in a dielectric resonator (manufactured by QWED), and the relative dielectric constant (Dk) and dielectric loss tangent (Df) at a frequency of 10 GHz were measured using a network analyzer (manufactured by Agilent Technologies, Inc., E8364B).

(Peel Strength)
The carrier film and the protective film were peeled off from the resin film, and H-VLP copper foil was superposed on both sides of the exposed resin layer. In this state, the copper foil was laminated to the resin layer using a vacuum pressure laminator (manufactured by Nikko Materials Co., Ltd., product name "V130") under conditions of a pressure of 0.9 MPa, a temperature of 100°C, and a pressure time of 60 seconds. Thereafter, the resin layer was cured by heating at 180°C for 60 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., product name "MSO-80TPS") to prepare a sample for peel strength measurement. The size of the sample was 10 mm wide x 70 mm long. The peel strength between the copper foil and the cured resin layer of the sample was evaluated using a tabletop peel tester (Shimadzu Corporation, product name "EZ-S"). The measurement conditions were a test angle of 90°, a peel speed of 50 mm/min, and the peel direction was the length direction of the sample.

(Combustion test)
The laminated film was heated in a dryer (manufactured by Futaba Scientific Co., Ltd., product name "MSO-80TPS") at 180°C for 60 minutes to harden the resin layer, thereby preparing a sample for a combustion test. The sample for the combustion test was subjected to a UL94V test.

1...base film, 3...resin layer. 10...laminated film.

Claims (8)

A substrate film and a resin layer provided on both sides of the substrate film,
The substrate film is a liquid crystal polymer film or a fluororesin film,
the resin layer includes a resin composition containing a rubber component, a cross-linking component having an epoxy group, a curing agent, a bromine-based flame retardant, and a flame retardant auxiliary;
the curing agent is an ester-based curing agent,
The content of the brominated flame retardant is 1 to 30 parts by mass per 100 parts by mass of the total amount of the rubber component, the crosslinking component, and the curing agent . The laminated film according to claim 1, wherein the bromine-based flame retardant includes a compound having a triazine skeleton. The laminated film according to claim 1 or 2, wherein the flame retardant auxiliary contains an antimony compound. The laminated film according to any one of claims 1 to 3, wherein the rubber component contains at least one rubber selected from the group consisting of acrylic rubber, isoprene rubber, butyl rubber, styrene butadiene rubber, butadiene rubber, acrylonitrile butadiene rubber, silicone rubber, urethane rubber, chloroprene rubber, ethylene propylene rubber, fluororubber, vulcanized rubber, epichlorohydrin rubber, and chlorinated butyl rubber. The laminated ...
The substrate film is a liquid crystal polymer film or a fluororesin film,
the cured resin layer includes a cured product of a resin composition including a rubber component, a cross-linking component having an epoxy group, a curing agent, a brominated flame retardant, and a flame retardant auxiliary;
The curing agent is an ester-based curing agent,
The content of the brominated flame retardant is 1 to 30 parts by mass per 100 parts by mass of the total amount of the rubber component, the crosslinking component, and the curing agent. The conductive substrate according to claim 5, wherein the bromine-based flame retardant includes a compound having a triazine skeleton. The conductor substrate according to claim 5 or 6, wherein the flame retardant auxiliary contains an antimony compound. The conductive substrate according to any one of claims 5 to 7, wherein the rubber component contains at least one rubber selected from the group consisting of acrylic rubber, isoprene rubber, butyl rubber, styrene butadiene rubber, butadiene rubber, acrylonitrile butadiene rubber, silicone rubber, urethane rubber, chloroprene rubber, ethylene propylene rubber, fluororubber, vulcanized rubber, epichlorohydrin rubber, and chlorinated butyl rubber.

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